The priority application Number Japanese Patent Application 2004-063474 upon which this patent application is based is hereby incorporated by reference.
1. Field of the Invention
This invention relates to a speaker apparatus, and more specifically to the speaker apparatus to be assembled easily, and of which coils generate high electromotive forces.
2. Description of the Related Art
Conventionally, a speaker apparatus having a light-emitting device in a visible position thereof, and the light-emitting device being lighted by a part of an input current for a voice coil are proposed for monitoring an input to the speaker apparatus. In such the speaker apparatus, a source for lighting the light-emitting device is supplied by a part of a voice-coil driving current, so that wiring between the light-emitting device and a feeder circuit for the voice coil is required.
FIG. 1 shows a half-sectional schematic view of a conventional speaker apparatus 9. The speaker apparatus 9 includes a magnetic circuit 10 having a cylindrical center pole 10a, a magnet 10b, and a yoke 10c. A magnetic gap 10d is formed in the magnetic circuit 10, and a voice coil 11 is inserted into the magnetic gap 10d. This voice coil 11 is wound around a coil bobbin 13 being supported movably in a vertical direction by a damper 12.
An inner periphery of a diaphragm 14 having a ring shape in a top view adheres to the coil bobbin 13. An outer periphery of the diaphragm 14 is fixed on a frame 19. A center cap 15 covers a center hole of the diaphragm 14. A coil bobbin 17 is formed integrally with a substrate on which a light-emitting device 16 is mounted. This coil bobbin 17 is attached to the center cap 15. An induction coil 18 is wound around the coil bobbin 17. Like the voice coil 11, the induction coil 18 is arranged in the magnetic gap 10d. 
According to the above, when the input current for the voice coil 11 is displaced, the coil bobbin 17 oscillates up and down. Owing to the oscillation of the coil bobbin 17, the diaphragm 14 and the center cap 15 oscillate to generate a sound. Further, the oscillation of the center cap 15 oscillates the induction coil 18 in the magnetic gap 10d, and the oscillation of the induction coil 18 induces an induced electromotive force. If this induced electromotive force is used for a source for lighting the light-emitting device 16, wiring between the light-emitting device 16 and a feeder circuit (not shown) for the voice coil 11 is not required.
However, in the speaker apparatus 9 of FIG. 1, the induction coil 18 is also inserted into the magnetic gap 10d to which only the voice coil 11 is originally inserted. Therefore, the magnetic gap 10d is needed to be larger, and the magnetic gap 10d cannot provide a large magnetic field to the voice coil 11 and the induction coil 18. Therefore, oscillations of the diaphragm 14 and the center cap 15 corresponding to the input current supplied to the voice coil 11 become so small as not to output a sufficient sound. Further, a high electromotive force cannot be induced through the induction coil 18. In addition, when assembling the speaker apparatus 9 on a production line, it is necessary to insert the two coils, the voice coil 11 and the induction coil 18, into the magnetic gap 10d. Therefore, there is a problem that an assembly operation of the speaker apparatus 9 is complicated.
Japanese published unexamined patent application No. 2003-23693 discloses a speaker apparatus (not shown) having an induction coil positioned outside of a magnetic gap as long as an induction coil receives a magnetic field of the magnetic gap. However, in such the speaker apparatus, it is more difficult for the induction coil to generate a high electromotive force.
Japanese published unexamined patent application No. 2000-261874 discloses a speaker apparatus (not shown) having an induction coil as a secondary coil corresponding to a voice coil as a primary coil. The induction coil generates an electromotive force to light a light-emitting device caused by a displacement of an input current to the voice coil. However, in such the speaker apparatus, it is necessary for a voice coil to pass a high input current for gaining a high electromotive force generated by the induction coil. Therefore, there is a problem to gain a high electromotive force.
In short, each of these conventional speaker apparatuses described above has two coils, a voice coil and an induction coil, for the one magnetic circuit. Therefore, there is a problem that a high magnetic field cannot be provided to either of the voice coil and the induction coil, and an assembly operation on a speaker apparatus production line is complicated.
Accordingly, it is an object of this invention to provide a speaker apparatus which is easily assembled, and in which coils generate high electromotive forces.